Apparatus for producing a hydrogen-rich and low carbon monoxide gas

ABSTRACT

A process for generating a high-hydrogen, low-carbon monoxide gas comprises generating a product gas in a gas generating device. The product gas contains hydrogen and carbon monoxide that are generated from catalytic water vapor reforming of a water/fuel mixture and/or from partial oxidation of an oxygen/fuel mixture. In a gas purification stage, the carbon monoxide fraction in the product gas is reduced by selective CO oxidation on an oxidation catalyst. During a starting phase, oxygen is admixed to the supplied fuel and the flow direction is reversed such that the flow first takes place through the gas purification stage and only then through the gas generating device.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This application claims the priority of German Patent ApplicationNo. 197 27 588.5, filed on Jun. 28, 1997, the disclosure of which isexpressly incorporated by reference herein.

[0002] The present invention relates to a process and a system forgenerating a high-hydrogen, low-carbon monoxide gas.

[0003] A system for generating hydrogen by means of partial oxidationand/or the water vapor reforming of methanol is known from German PatentDocument DE 44 23 587 C2. In addition to containing hydrogen, thereforming product gas flow also contains carbon monoxide which isundesirable for certain applications, for example, during the conversionof the generated hydrogen in a fuel cell.

[0004] For eliminating or at least reducing the carbon monoxide fractionin the high-hydrogen gas, it is also known to connect a gas purificationstage behind the gas generating device. Such a gas purification stage isknown, for example, from German Patent Document DE 195 44 895 C1, inwhich the carbon monoxide contained in the high-hydrogen gas isselectively oxidized with the addition of oxygen on an oxidationcatalyst.

[0005] During starting, the gas generating system must be brought to theoperating temperature. This can take place, for example, by heating fromthe outside or by introducing hot gases. From Japanese Patent DocumentJP 58-108291 A, it is known, for example, to provide a ceramic core withan electric heating device in a reformer. For generating hot gases, forexample, a catalytic combustion on a Pt-containing catalyst can be used.From Japanese Patent Document JP 08119602 A, a gas generating system isknown, for example, which has a separate catalytic burner. A hot gas isgenerated there whose energy is transmitted in an evaporator to the gasto be reformed and thus, during the flow through the reformer, is alsotransmitted to the reformer. A disadvantage of these systems is the factthat additional components are required for the heating, particularly inthe starting phase.

[0006] It is an object of the present invention to provide a process andapparatus for generating a high-hydrogen, low-carbon monoxide gas withimproved cold-starting characteristics.

[0007] This problem is solved by a process and a system according to thepresent invention.

[0008] During the normal operation of a gas generating system, the gasflows through a gas purification stage only after it has flowed throughthe gas generating device. If a system for the selective CO-oxidation isused as the gas purification stage, which generally contains aplatinum-containing catalyst for removing the carbon monoxide from thehigh-hydrogen gas, the system can temporarily be operated as a catalyticburner during the starting phase in a simple manner by a reversal of theflow direction so that the gas generating system can easily and rapidlybe brought to the necessary operating temperature. Additionalcomponents, apart from corresponding switching valves, are not requiredfor this purpose. Thus, a compact system is created.

[0009] If this flow reversal principle is used in a gas generatingdevice in which, in addition to or instead of the water vapor reforming,partial oxidation is also carried out, another advantage results. Aplatinum-containing zone which in the normal operation is disposed infront of the reforming area would necessarily lead to a two-stage methodof operation. In the normal operation, the oxygen in the gas flow wouldbe completely consumed in the platinum-containing zone, which is highlyactive for the combustion. As a result, large amounts of heat arereleased in the platinum-containing zone which must be transported intothe reforming area. Should this two-stage operating method not bedesired, the flow through the platinum-containing zone is permitted onlyduring the starting phase, which would result in an exclusive use ofthis component for the starting phase.

[0010] In contrast, by means of the system and process according to thepresent invention, a simple solution is obtained without a separatereactor or reactor area which is used only during the starting phase.

[0011] Other objects, advantages and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a basic diagram of a system for generating ahigh-hydrogen, low-carbon monoxide gas with the valve shifting positionsduring normal operation; and

[0013]FIG. 2 is a view of the system of FIG. 1 with the valve shiftingpositions during a starting phase.

DETAILED DESCRIPTION OF THE DRAWINGS

[0014] The system for generating a high-hydrogen, low-carbon monoxidegas indicated as a whole by reference number 1 in FIG. 1 and in thefollowing called gas generating system, consists of a gas generatingdevice 2 and of a gas purification stage 3. The gas generating device 2may be constructed as a reactor for the catalytic water vapor reformingof a water vapor/fuel mixture (i.e, “reformer”), or as a reactor for thepartial oxidation of an oxygen/fuel mixture. In addition, it is alsopossible to integrate the reactor for the partial oxidation in thereformer in that a suitable oxidation catalyst is preferably arranged inthe inlet area of the reformer.

[0015] The gas purification stage 3 is constructed as the device for theselective carbon monoxide oxidation (i.e., “CO-oxidator”). In normaloperation, the product gas is guided from the gas generating device 2directly into the gas purification stage 3. The gas generating system 1is preferably constructed as a heat exchanger, a heat exchanger surface16 being provided between the gas generating device 2 and the gaspurification stage 3. Any hydrocarbon-containing starting substances canbe used as fuel, the following embodiment being explained by means ofmethanol as the fuel.

[0016] A gaseous water vapor/methanol mixture is supplied to the gasgenerating device 2 by way of a feed pipe 6. For generating the watervapor/methanol mixture, an evaporator 17 is provided to which water andliquid methanol is supplied from corresponding storage tanks 20, 21 bymeans of delivery pumps, which are not shown, by way of correspondingpipes 18, 19. For the metering of the media, or for theactivating/deactivating of the delivery, metering valves 22, 23 areprovided in the pipes 18, 19. The water vapor/methanol mixture generatedin the evaporator 17 is then, in the normal operation, by way of thepipe 8 and the two-way valve 4 fed into the pipe 6. In this switchingcondition of the two-way valve 4, the connection between the pipe 6 anda pipe 10 is interrupted. If an oxidation catalyst is provided in thegas generating device 2, a suitable amount of oxygen or air is meteredto the water vapor/methanol mixture by way of an oxygen supply pipe 15with an integrated metering valve 24.

[0017] During the catalytic water vapor reforming of methanol, whileheat is supplied, a mixture of methanol and water vapor is converted tohydrogen on a suitable catalyst; carbon dioxide and carbon monoxide aregenerated simultaneously:

CH₃OH+H₂→3H₂+CO₂ or CH₃OH→2H₂+CO

[0018] As an alternative, or in addition, methanol may also be convertedwhile adding oxygen by a partial oxidation to carbon dioxide andhydrogen:

CH₃OH+½O₂→2H₂+CO₂

[0019] The CO oxidator 3 is used for removing CO, by means of aselective oxidation of carbon monoxide, from the high-hydrogen gasgenerated in the gas generating device 2. The product gas consisting,for example, of hydrogen and carbon dioxide with a CO fraction of 1-3%by volume, after a corresponding purification, is preferably used forthe mobile application of PEM fuel cells in vehicles.

[0020] In the case of the partial or selective oxidation, oxygen is alsoadded to the product gas, for example, in the form of ambient air, inwhich case the carbon monoxide CO is then oxidized by the oxygen O₂ tocarbon dioxide CO₂:

CO+½O₂→CO₂

[0021] As an alternative, the oxygen can also be charged at one orseveral points directly into the CO oxidator 3, for example, by way ofan additional pipe which, however, is not shown in the embodiment. Thereaction is carried out on a suitable oxidation catalyst, such asplatinum and/or ruthenium, on a suitable carrier, such as Al₂O₃ or azeolite in powder form. After the purification of the product gas, thehigh-hydrogen, low-carbon-monoxide gas is then removed by way of thepipe 7, the two-way valve 5 and the pipe 11 to a receiver which is notshown, such as a storage device or a fuel cell.

[0022] Furthermore, the storage tank 21 for the methanol is connected byway of another pipe 9 with the two-way valve 5. However, in the normaloperation, this pipe 9 is blocked by the two-way valve 5. In addition, asecond oxygen feed pipe 14 with an integrated metering valve 25 isprovided on the pipe 9. Finally, for controlling the whole system, acontrol apparatus 12 is provided which is connected with the valves 4,5, 22-25 by way of control lines.

[0023] During the normal operation, the two-way valves 4, 5 are held inthe illustrated position of FIG. 1 by means of the control apparatus 12.The metering valve 25 is closed. The positions of the metering valves 22to 24 are adjusted corresponding to a load demand.

[0024] The water vapor reforming is an endothermal reaction. This meansthat energy must be continuously supplied to the reformer formaintaining the reaction. Since the CO oxidation is a highly exothermalreaction, the reformer 2 and the CO oxidator 3 are preferably integratedin a common housing so that the energy released in the CO oxidator canbe transmitted to the reformer 2 by way of the heat exchange surface 16.Naturally, it is also possible to heat the reformer separately by a heatexchanger integrated in the reformer so that the integration in a commonhousing is unnecessary.

[0025]FIG. 2 illustrates the device explained in FIG. 1 in the switchingposition during the starting phase, in which case, with respect to FIG.1, the same parts have identical reference numbers.

[0026] During the start, the control apparatus 12 brings the two-wayvalves 4, 5 into the illustrated switching positions. Simultaneously,the metering valves 22 to 24 are closed and the metering valve 25 isopened. As a result, no more water and methanol is supplied to theevaporator 17 or into the pipe 8. On the contrary, methanol and oxygen,which is supplied by way of line 14, are fed by way of the two-way valve5 and the pipe 7 into the CO oxidator 3 and oxidized there on the COoxidation catalyst. The CO oxidator with the oxidation catalystcontained therein is therefore temporarily used as a catalytic burner.By means of this catalytic oxidation, thermal energy is released. Thehot gas will then flow through the gas generating device 2 which, as theresult, is rapidly brought to the operating temperature. After flowingthrough the gas generating device 2, the gas is then by way of the pipe6, the two-way valve 4 and the pipe 10 discharged into the environmentor to a catalyst, which is not shown, for utilizing the residual gas. Bymeans of the switching operations initiated by the control apparatus 12,the flow direction in the gas generating system is therefore reversed inthe starting phase in comparison to the normal operation.

[0027] The starting phase is terminated, for example, after a definedtime period or when a defined temperature in the system 1 is reached.The feeding of the fuel/oxygen mixture to the CO oxidator 3 will then bestopped by means of the control apparatus 12 by triggering the valves 4,5, 22 to 25. Subsequently, the gas generating system 1 will then beoperated in the above described manner.

[0028] In addition to the arrangement illustrated in the drawing, otherembodiments are also conceivable. For example, the pipe 9 and the secondoxygen supply pipe 14 can be eliminated. Instead, between the mouth ofthe oxygen supply pipe 15 and the two-way valve 4, a bypass pipe canbranch off pipe 8 which is then, instead of pipe 9, connected with thetwo-way valve 5 for supplying a methanol/oxygen mixture during thestarting phase. In this case, during the starting phase, water can thenalso be metered in from the storage tank 20.

[0029] Furthermore, the gas generating device 2 as well as the gaspurification stage 3 can be constructed in several stages, in whichcase, in the starting phase, the flow can take place through one orseveral stages in the reversed flow direction. It is only important thatthe flow first takes place through the stages of the CO oxidator 3 andthis stage will then be used as a catalytic burner. In the illustratedembodiment, in the starting phase, not only the sequence of thecomponents 2, 3 is exchanged but the flow direction within thecomponents 2, 3 is also reversed. However, it is also conceivable toexchange by means of a suitable guiding of the pipes the sequence of thecomponents 2, 3 during the starting phase but to maintain the flowdirection within the components 2, 3.

[0030] The foregoing disclosure has been set forth merely to illustratethe invention and is not intended to be limiting. Since modifications ofthe disclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A process for generating a high-hydrogen,low-carbon monoxide gas, comprising: admixing oxygen with fuel; flowingsaid admixture through a gas purification stage; catalytically oxidizingsaid admixture to form a hot gas; flowing said hot gas through a gasgenerating device to bring said gas generating device to an operatingtemperature; after said gas generating device is brought to theoperating temperature, flowing at least one of a water and fuel mixtureand an oxygen and fuel mixture through the gas generating device to forma product gas that contains hydrogen and carbon monoxide; and flowingthe product gas through said gas purification stage, thereby reducingthe carbon monoxide fraction in the product gas.
 2. The processaccording to claim 1 , wherein said product gas is generated bycatalytic water vapor reforming of said water and fuel mixture.
 3. Theprocess according to claim 1 , wherein said product gas is generated bypartial oxidation of said oxygen and fuel mixture.
 4. The processaccording to claim 1 , wherein said reducing is by a selective COoxidation on an oxidation catalyst.
 5. The process according to claim 1, wherein during a starting phase, the flow takes place through the gasgenerating device and the gas purification stage in a respectivelyreversed direction.
 6. The process according to claim 1 , wherein duringa starting phase, the flow direction in one of the gas generating deviceand the gas purification stage is maintained and only a sequence of theflow through said device and said stage is exchanged.
 7. An apparatusfor generating a high-hydrogen, low-carbon-monoxide gas, comprising: agas generating device for forming a product gas by at least one ofcatalytic water vapor reforming of a water vapor and fuel mixture andpartial oxidation of an oxygen and fuel mixture; a gas purificationstage for removing carbon monoxide from the product gas by means ofselective CO oxidation; and feed and discharge pipes for reversing aflow direction through said gas generating device and said gaspurification stage by way of valves.
 8. The apparatus according to claim7 , wherein during a starting phase, the gas generating device isarranged downstream of the gas purification stage and, after theconclusion of the starting phase, the gas purification stage is arrangeddownstream of the gas generating device.
 9. The apparatus according toclaim 7 , further comprising an oxygen feed pipe for adding oxygen intoa fuel feed pipe at least during the starting phase.
 10. The apparatusaccording to claim 7 , wherein the valves, are two-way valves, eachconnected with a pipe for feeding a fuel to either said gas generatingdevice or said gas purification stage and each connected with a pipe fordischarging a gas from said gas generating device or said gaspurification stage.
 11. The apparatus according to claim 10 , furthercomprising a control apparatus for triggering the two-way valves suchthat, during a starting phase, said fuel feeding pipe to said gaspurification stage and said gas discharging pipe from said gasgenerating device purification pipe are in a flow-type connection and,after conclusion of the starting phase, said fuel feeding pipe to saidgas generating device and said gas discharging pipe from said gaspurification stage are in a flow-type connection.